This invention relates in a first aspect to a dispensing device for storing and applying at least one liquid or pasty substance, which device generally comprises a housing equipped with a dispensing nozzle attached thereto; at least one cartridge being provided with a discharge outlet and with at least one piston for expelling a quantity of the aforesaid substance from the cartridge. More particularly, the invention relates to a dispensing device of the above-described kind, wherein the cartridge is manufactured at least partially from cuttable material; at least two pistons are separated from each other by a cartridge wall and are connected with each other by a coupling unit for joint displacement; and at least one cutting member is mounted behind a forward end plane of the pistons and serves for cutting through the cuttable cartridge wall between the pistons.
In another aspect, the invention relates to a method of using a dispensing device of the above-described particular kind for discharging at least two components with the aid of a propellant of low excess pressure.
Two- or multi-component systems in which two or more substances are stored separately, are mixed each time a quantity thereof is being discharged and are applied to a desired site are being used increasingly as dispensers for adhesives, fillers, foam formers for filling shipping boxes and the like packings for goods susceptible to shock, for the coating of surfaces and for related purposes
It is of special importance in the case of known two-component adhesives that a mixing ratio with 10% tolerance is strictly maintained and that both components are being thoroughly mixed with each other. Experience has shown that this rule is frequently being sinned against, due to the fact that the components are sold and stored in tubes. During application, the user discharges the contents of the tube on to a surface, for instance a piece of paper or a plate-like vessel and mixes the components with a stirring rod. Mixing errors will occur especially when only a small amount of adhesive is required, or the components are not being mixed intimately enough. Consequently, the adhesive mixture will not harden properly and the glued parts will not hold together. If the adhesive mixture does not contain enough hardener, it may moreover have a strongly corrosive effect. But even when the preparation is carried out correctly, this method of gluing suffers from certain drawbacks. The various processing steps require much time, in particular the manual mixing of components, and may constitute a cost factor which is not to be neglected. The component mixture being prepared is openly accessible to the air and thus easily contaminated, and the antire handling is therefore objectionable also from a point of view of occupational hygiene. Thus, contact of the hardener with the user's skin may cause dermatoses.
In French Pat. No. 2,501,080 and in U.S. Pat. No. 4,366,919, there have been described apparatus possessing some of the features of the initially-described particular device. In the device according to French Pat. No. 2,501,080, an exit channel unit is provided between the forward end of the cartridge and the rearward connecting end of the discharge nozzle, through which unit the components are transferred from individual cartridge chambers via separate ducts to the mixing nozzle. Chamber exit orifices of an external chamber are constituted by two diametrically oppositely located passages from which two channels lead radially to the center of the cartridge and from there via an exit channel for the respective component which passes from the central chamber through the latter into a mixing chamber.
Indeed, the known devices mitigate in a certain manner the above-described problems which arise when mixing and dosing the above-mentioned components. Nevertheless, these known devices still suffer in particular from the following drawbacks:
Due to the different viscosities of the components and on account of frictional forces occurring in view of the differently designed pistons of different size, these pistons, acted upon by compressed air of equal pressure, will travel through paths of different length. In order to maintain an exact mixing ratio, it is however required that the pistons travel through paths of equal length. This is only possible if there exists a mechanical connection between the pistons which must be designed in a manner such that it will still exist when the pistons have arrived at the forward end of the cartridge. For this reason, the known devices require structural parts to the rear of the cartridge which correspond approximately to the lengths of the cartridge itself and thus render the entire device heavy and unwieldy.
In another device which is known from German Offenlegungsschrift No. 25 21 392, the space required by the coupling means of the pistons has been considerably reduced. In this device, the interior of the cartridge is subdivided by a cartridge wall constituting a dividing wall which extends longitudinally in the cartridge. This dividing wall is cut open by cutting means moving ahead of the piston which are provided with slots through which the cut-apart portions of the dividing wall are guided. A bridge member serves as piston coupling means holding together the piston which is divided almost completely into two parts, and also carries the cutting blade. This bridge member is provided with suitably designed guiding means permitting the cut-apart portions of the dividing wall to be guided past the bridge.
This complicated construction of the piston-coupling means requires special means for deflecting the cut-apart portions of the dividing wall, thus occupying a considerable share of the available space in the interior of the housing. Moreover, the deflection of the dividing wall parts consumes valuable discharge pressure. This can become problematic in particular in the case of propellant-operated piston dispensers, as official safety regulations permit only relatively low propellant pressures. Furthermore, the deflection process causes a strong deformation of the cartridge walls which are anyhow under severe stress, and leads to problems with regard to the sealing properties of the discharge pistons.
A similar device is described in European Pat. No. 119,847 and comprises two chambers which are formed in a cylindrical housing by a flexible dividing wall which extends longitudinally through the housing and is fastened to the walls of the latter. This dividing wall is cut away or asunder by means of a plunger actuated by a piston of complicated structure, and is moved or stored out of the way in a space rearward of the piston in order not to impede the further advance of the piston. Again, the complicated piston structure, the loss of available space in the housing interior and the increased consumption of operational pressure for actuating the deflecting means for the cut-apart dividing wall portions constitute drawbacks of this known device.
A further problem occurring with the known devices arises in connection with the design of their units for exiting the respective components or substances. For reasons of convenience, their front discharge ends are often left open, especially when the dosing step is only to be interrupted for a short time. However, it is a fact that the individual components show different exiting behavior or leaking when the pistons are not being actuated. A low viscosity substance having many occlusions of air tends more easily to leaking than a highly viscous substance free from occluded air. When the discharge device is left to lie about with its exit orifices open it may happen, for instance, that the hardener will leak from the mixing nozzle when the reactive resin will not do so. This will lead to a disturbed dosing ratio of the components at the very beginning of the next discharge, with all disadvantagesdiscussed further above. Not only will this cause the mixture to be highly corrosive but it will also fail to maintain, for instance, the adhesive strength of an adhesive mixture. Such a device would, however, not be admissible for use in the construction and the repair of vehicles and would be refused approval by a government testing authority.
It is indeed known from the European Pat. No. 105,181 to provide in the exiting unit a valve to be actuated separately from the discharge of the components. However, the manual operation of such a valve would obviously be a complicated one.